Free Online Utility Tools for Web Developers

My list of free online tools useful for web development

Online practice, test, and share

http://cssdeck.com
http://liveweave.com/
http://jsbin.com/
http://jsfiddle.net/
http://tinkerbin.com/
http://codepen.io/
http://plnkr.co/
http://dabblet.com/

·        https://htmlcodeeditor.com

·        https://www.w3schools.com/tryit/

·        https://htmledit.squarefree.com

·        https://html5-editor.net

·        https://htmleditor.tools

https://htmleditor.io
https://htmleditor.tools/html-editor/ 

Multi-service

http://www.freeformatter.com/

Website review and analysis

http://www.woorank.com/en/www/

http://iwebchk.com/

http://builtwith.com/

https://wappalyzer.com/

Validation and debugging

http://validator.w3.org/
http://html5.validator.nu
http://www.modern.ie/en-us/report
http://www.csstrashman.com
http://jsonlint.com/

Crawling and monitoring

http://web-sniffer.net/
http://gsnedders.html5.org/outliner/

Code generators

http://www.visualcsstools.com/: including CSS and SVG
http://css3generator.com/
http://cssmenumaker.com/
http://www.css3maker.com/
http://www.css3.me/
http://html-color-codes.info/
http://www.colorzilla.com/gradient-editor/
http://gradients.glrzad.com/
http://cubic-bezier.com
http://matthewlein.com/ceaser/
http://www.roblaplaca.com/examples/bezierBuilder/
http://ie.microsoft.com/testdrive/graphics/hands-on-css3/: has a number of good visual generators.
https://code.google.com/p/svg-edit/
http://dataurl.net
http://toolspot.org/data-uri-generator.php
http://stylebootstrap.info/

Mobile and responsive design preview:

http://www.mobilephoneemulator.com/
http://ipadpeek.com/
http://responsivepx.com
https://quirktools.com/screenfly/
http://www.responsinator.com/
http://responsive.is
http://mattkersley.com/responsive/
http://dfcb.github.io/Responsivator/

Reference

http://www.quirksmode.org/compatibility.html
http://ascii.cl/htmlcodes.htm
http://www.w3schools.com/tags/ref_symbols.asp